The present invention is related to pistons used to dispense commodity material from storage, processing and transport containers.
More and more industrial companies are using commodity materials in their manufacturing processes that will prematurely cure if exposed to air or moisture and/or that have chemical vapors that must be contained. Some of these materials are highly viscous or are fluids that must be evenly dispensed into processing equipment without fluctuations in the flow. Some pumps can cause even the most minor of fluctuations in the flow of material that is still too much variation for the sensitivity of some production equipment. Further, many of the materials used in manufacturing are blended with very expensive compounded chemicals. Also, it is very expensive to dispose of or to recycle chemical residues, and any loss of material adds to the cost of manufacturing. Therefore, commodity material consumers need the ability to fill a tank and then remove almost all of the viscous, non-flowable, sensitive material out of a tank without ever opening the tank and/or to push material at an even flow rate out of the tank without a pump.
One method practiced by the industry to dispense material from the tank is to use a piston inside of the tank that is pushed through the tank during the dispensing process by the use of pressurized air, nitrogen or any other gas. The piston moves in the opposite direction when the tank is filled with material by the material itself pushing the piston in the opposite direction. Any air, nitrogen or any other gas is vented out of the tank during the re-filling operation.
Generally, it is known that tanks with dispensing pistons can be used to dispense a wide range of materials, ranging from non-flowable materials to low viscosity liquids. Also, the tanks can be as small as drums and as large as a bulk storage tank. The tanks can be stationary, or moveable by such methods as, but not limited to, fork lift trucks, trucks, rail, ship, airplanes.
Generally, tanks with dispensing pistons have been used for many years. These pistons were designed originally for use in large trailerable tank trucks.
Such trailerable tanks are large in diameter, approximately 68 inches. Often the interior surface of these tanks is not perfectly round the whole length of the tank, and the tanks are made to flex as the tanks are pulled down the highway. This flex can cause distortion of the interior diameter surface inside of the tank over time. Therefore, the dispensing pistons that were previously designed for the trailer tank trucks had to take this into consideration.
The previous design required that the diameter of the rigid portion of the piston member could not be made with close dimensional tolerances to the inside diameter dimension of the tank wall. Because the diameter of such pistons were much smaller than the inside diameter of the tank wall, canting of the piston during dispensing and filling of the tank was a problem that required the use of anti-canting pads, rings and/or other materials on the outside surface of the piston. Those anti-canting devices prevent the piston from slanting inside of the tank and becoming stuck in the tank. For example, if the diameter of the piston body is approximately 65 inches and the interior diameter of the tank is approximately 68 inches, the thickness of the anti-canting pads would have been approximately 1 1/4 inches.
Unfortunately, the use of pistons with anti-canting devices has numerous disadvantages. First, these pistons with large gaps between the tank wall and the piston impose greater stress and shear on the seals, because the seal has to extend far beyond the piston periphery to contact the tank wall. Second, most anticanting devices are static and cannot automatically compensate for the various dynamic forces that occur inside of the tank during the dispensing process. Another disadvantage is the added cost and complexity of manufacturing attributed to the manufacture and assembly of the anti-canting devices. Therefore, there is a need for a piston that avoids the disadvantages attributed to anti-canting devices, and can efficiently dispense practically all of the commodity material from a container while maintaining a tight seal without canting during the dispensing process.